Conventionally, papermaker's felts have been formed by weaving a fabric base and then needling fibrous batts to the base. The use of woven fabric has certain disadvantages. The fabric is normally woven in endless configuration on a loom and due to the size of the felt, a very lengthy set-up time is required before the weaving operation can begin. When fabricating felts of substantial size, it may take a group of workmen several days to set up the loom before weaving can commence. Furthermore, since felts are generally becoming larger, the size of the loom required is also becoming larger.
The shuttle, which is used in the conventional weaving operation to interleaf the cross yarns with the warp yarns, is only capable of containing a limited quantity of yarn and after deletion of the yarn, additional lengths of yarn must then be overlapped with the trailing end of the original length, resulting in pressure points in the completed felt.
As a further problem, the normal weaving process produces distortion of the yarns at the side edges of the woven fabric and non-uniformity in spacing between the yarns. The non-unifornity must normally be corrected through tedious manual operations.
A further disadvantage of utilizing a woven fabric in a papermaker's felt is that the points of crossover between the cross yarns and the warp yarns act as pressure points and can cause disfiguration of the paper web. It has also been recognized that cross yarns impede the drainage characteristics of the felt which can adversely affect the felt's performance on the papermaking machine.
To overcome the disadvantages of the woven base fabric, U.S. Pat. No. 4,495,680, granted Jan. 29, 1985, discloses a method and apparatus for forming a substrate composed solely of machine direction or longitudinal yarns. In accordance with the invention of the aforementioned patent application, a plurality of yarns or strands are drawn from a supply and wound about a pair of parallel rolls in a helical pattern by a traveling winder member. The winding member is connected to a loop which extends around the rolls and the yarns are attached to the trailing end of the winding member. As the rolls rotate, the winding member travels in a helical path around the rolls to thereby draw the yarns from the supply and wind the yarns in a helical pattern about the rolls. Spacing members, such as combs, are located parallel to the rolls and maintain proper spacing and order of the yarns as they are wound about the rolls.